Why Do The Leaves Of The Marijuana Plant Turn Yellow?

Are some or all of your cannabis leaves turning yellow? Maybe your leaves also have other symptoms like spots, curling, wilting, brown patches, etc. Marijuana plants may get yellowing leaves for several different reasons, so it can be hard to figure out the true root of the problem!

Here are four reasons your weed leaves are yellowing and and how to deal with them properly for a heavier harvest.

PH and Nutirent lockout

Soil growers have the advantage of cultivating in a medium, that acts as a buffer for roots. Hydroponics and coco are not quite as forgiving to pH imbalances. Even soil growers need to at least come close to getting the ideal pH of 6.0-7.0 and maintain it, otherwise plants will suffer. 5.5 to 6.5 pH is generally agreed upon as the recommended range for hydro and coco. Yellow leaves can be a warning sign, that you don’t have your nutes dialled in and the pH is off.

Essentially when the pH of your nutrient solution strays above or below the particular sweet spot for your substrate, it prevents complete absorption of all the elements of the solution. Roots are starved of certain nutrients and micronutrients as the incorrect pH causes a lockout.


Solution: Invest in a pH pen or cannabis fertilisers with pH-perfect solutions, that can auto adjust a wider pH range. Flush plants with pure water and then resume feeding with a light dialled in solution to suit your growing medium. Also, make sure that the base nutrients you use contain all of the essential microelements or you will have to add extra bottles of supplements to the budget.

Light Burn

Symptoms

• Yellowing appears most on the parts of the plant closest to the cannabis grow light.
• Yellow leaves do not pull out easily, even if the whole leaf is dead
• Light burn often takes a few weeks to develop and is most common once the plant is past the 6th week of the flowering stage (when plants aren’t making many new leaves to replace old ones).

Cannabis light burn usually affects the top leaves closest to the grow light instead of affecting the plant evenly

How Do Growers Get It?

• Light burn is when your leaves are working too hard for too long, causing them to die early.
• Even if the temperature is in a good range, your plant can still get light burn if the grow light is too close. It’s kind of like how skiers can get sunburned even in the freezing temperatures because of all the sunlight reflecting off the snow.
• Light burn is most common with powerful LED grow light and HPS grow lights.
• It’s also common when switching to new bulbs (which are stronger than old bulbs) or when there is no glass between the bulb and your plants.
• Some plants are more sensitive than others, and you may have one plant suffering from light burn while the others are fine. That can make it harder to diagnose the problem since some of your plants are thriving in the same environment!

Light burn symptoms can be different from plant to plant, but they always seem to happen mostly to the parts of the plant that are closest to the light

Solution: 

• The best way to fix light burn is to move you grow lights further away, or bend over the affected plants so they’re further from the light.
• When in doubt, always follow the manufacturer’s recommendations when it comes to how far away to keep your light from your plants! This is especially important for growers who utilize Full spectrum LED grow lights.

Over or Under-Watering

Plants experiencing either over or under-watering will exhibit noticeable symptoms for new to experienced growers to quickly notice. The most common symptom will be drooping from either action. Over-watering will cause the leaves appear swollen and over-concentrated with water. This is most common with young plants due to their undeveloped root system and will later affect its flowering stage. Under-watering makes the leaves appear papery and brittle from lack of water running through its veins. Continued under-watering will cause the plant to turn yellow and lose leaves to save energy. An important thing to acknowledge is adjusting watering levels to the plant/container ratio. This issue is often overlooked and needs to be personalized to every growers specific needs.

Solution: Decreasing water flow to over-watered and increasing water to under-watered sounds easy in practice, but will take thoughtful consideration from the grower to find the perfect ratio. Make sure to find right sized container and always check the bottom of the plant to see how damp the soil is after watering.

Nutrient Deficiency

If all other factors are in balance—light, water and pH—then the most likely culprit is a lack of food for your plants. Nitrogen and iron are the most common deficiencies that cause yellowing leaves, but it could be any number of macro or micronutrients as well.

Solution: Water with a nutrient solution high in nitrogen. Plant food bottles typically display NPK ratio on the labels. N is for nitrogen, P for phosphorus and K for potassium. Choose the nutrient with a higher number at the beginning. They’re labels will say “Grow” or “Vegetative” as opposed to “Bloom” or “Flowering.” If you decide you have a lack of iron, foliar feed with chelated iron. You should see your leaves greening up within a few days.

Also in Indoor Growing Guides